Quaternary Structure of Protein: Definition & Overview

Lesson Transcript
Instructor: Shannon Compton

Shannon teaches Microbiology and has a Master's and a PhD in Biomedical Science. She also researches cancer and neurodegenerative diseases.

Proteins have four levels of structure: primary, secondary, tertiary, and quaternary. The first three involve only one molecule. However, quaternary structure describes how proteins interact to form complex molecular structures.

What is a Quaternary Protein Structure?

By definition, quaternary structure is the arrangement of more than one protein molecule in a multi-subunit complex. The nomenclature here can get a bit confusing because we call a single polypeptide chain a protein if it can function on its own. However, many proteins are actually comprised of several polypeptide chains. In this case, the individual peptide chains are called protein subunits, and they cannot function on their own.

Protein subunits come together to form a protein
Quaternary protein structure

This image shows a protein that is made of several protein subunits. Each color represents a separate protein. Each protein subunit is produced individually by a ribosome. Then, each protein subunit attains secondary and tertiary structure. Finally, the protein subunits come together to form a fully functional protein.

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Secondary Structure of Protein: Definition & Overview

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
 Replay
Your next lesson will play in 10 seconds
  • 0:00 Quaternary Protein Structure
  • 0:50 Proteins with this Structure
  • 1:40 Functions of this Structure
  • 2:05 Homo- vs. Heteromultimeric
  • 3:00 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Timeline
Autoplay
Autoplay
Speed Speed

Proteins with Quaternary Structure

An example of a protein with quaternary structure is hemoglobin. In hemoglobin, one protein binds to oxygen while another binds carbon dioxide. This is how one protein can serve two functions.

Enzymes can consist of a single protein or multiple protein subunits. Holoenzymes are those with several subunits. Each subunit of a holoenzyme has a different function. For example, one protein subunit may be the regulatory subunit. Enzymes can also be referred to as multimeric. Another protein subunit may be the catalytic subunit. Another name for a protein with quaternary structure is called a multiprotein complex. Microtubules, which act like highways in your cells, are multiprotein complexes.

Functions of Quaternary Structure

As mentioned above, quaternary structure allows a protein to have multiple functions. It also allows for a protein to undergo complicated conformational changes. This has several mechanisms. First, an individual subunit can change shape. In addition, the subunits can change their orientation with regard to one another. A multimeric protein can do either one of these, or it can do both. These conformational changes allow for a high degree of regulation. They are also key to a multimeric protein's ability to perform its physiological function.

To unlock this lesson you must be a Study.com Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back
What teachers are saying about Study.com
Try it now
Create an account to start this course today
Used by over 30 million students worldwide
Create an account